Greenhouse Gas Measurements Research Articles

Integrating project-based infrastructures with long-term greenhouse gas observations in Africa

There is a lack of long-term greenhouse gas (GHG) measurement infrastructures in Africa. This limits our understanding of the temporal dynamics of the biosphere-atmosphere exchange of carbon in response to climate change. Where relevant infrastructures have been established in externally funded research projects, they have often not been successfully transferred to local institutions at project termination, nor maintained in the long term. This leads to loss of capacity and continuity in primary data. We describe a collaborative approach where eddy-covariance (EC) towers for continuous long-term observation of carbon dioxide and energy fluxes were constructed under two consecutive German-funded research projects and designed to complement existing South African infrastructures. They will be transferred to partner institutions at project termination, supported by deliberate capacity building actions for long term sustainability. Joint activities were implemented to i) strengthen technical expertise for infrastructure maintenance, ii) introduce new generation of academic scientists to the topic, iii) co-develop a training concept to enhance local capacity to continue teaching the topic, iv) improve the uptake and use of data by the research community, v) improve data use and access by stakeholders, and vi) facilitate knowledge exchange between institutions. Co-designed activities included training, apprenticeships and knowledge exchange, student exchange, co-supervision, and public outreach. Following a similar model in international research projects could significantly benefit 1) national capacity for emission inventories, 2) development of long-term GHG observation networks, and 3) the global scientific community via improved availability of data. While we specifically focus on a network of GHG observations, the principles are applicable for the infrastructure to observe other surface/atmosphere exchange processes or other long term observational infrastructure.

The first simultaneous and continuous underway measurements of atmospheric gaseous elemental mercury, carbon dioxide and methane in the marine boundary layer: Results of cruise study in the Sea of Japan in May 2018

This paper presents the results of the first simultaneous measurements of gaseous elemental mercury (GEM) and greenhouse gases (CH4 and CO2) in the marine boundary layer over the Sea of Japan. Continuous underway measurements of atmospheric GEM, CH4 and CO2 concentrations were carried out aboard the R/V Akademik M.A. Lavrentiev from 4 to May 26, 2018. GEM concentrations (range: 0.4–1.6 ng/m3; mean ± standard deviation (SD): 1.0 ± 0.2 ng/m3; N = 938) were lower than both the atmospheric background and previously observed values in this area. Concentrations of CH4 (range: 1922.6–2010.6 ppb; mean ± SD: 1942.2 ± 10.8 ppb) and CO2 (range: 408.9–436.1 ppm; mean ± SD: 412.5 ± 2.5 ppm) were higher than both the average global atmospheric concentrations in May, and the average annual values. Concentration-weighted trajectory (CWT) analysis highlighted the Korean peninsula, northeastern China, southern Primorsky Krai (Russia) and the southwestern coast of Hokkaido (Japan) as potential source areas influencing atmospheric GEM, CH4 and CO2 concentrations during the cruise. Vertical distribution of the CWT values for all the measured gaseous species identified the lower atmosphere up to 1000 m as source layer. The same layer was also characterized by lower CWT values for CH4 and CO2, which were associated with atmospheric transport from the central part of the Sea of Japan. With increasing altitude, the CWT values for GEM and CH4 decreased, while the CO2 values began to rise from 2000 m reflecting the respiration of terrestrial ecosystems and, possibly, atmospheric transport from fires in western Russia.The study shows potential source regions influencing GEM, CH4 and CO2 concentrations in the atmosphere over the Sea of Japan in May 2018.

Methane, carbon dioxide, hydrogen sulfide, and isotopic ratios of methane observations from the Permian Basin tower network

Abstract. We describe the instrumentation, calibration, and uncertainty of the network of ground-based, in situ, cavity ring down spectroscopy (CRDS) greenhouse gas (GHG) measurements deployed in the Permian Basin. The primary goal of the network is to be used in conjunction with atmospheric transport modeling to determine methane emissions of the Delaware sub-basin of the Permian Basin oil and natural gas extraction area in Texas and New Mexico. Four of the measurements are based on tall communications towers, while one is on a building on a mountain ridge, with the recent addition of a small tower at that site. Although methane (CH4) is the primary species of interest, carbon dioxide (CO2), hydrogen sulfide (H2S), and the isotopic ratio of methane (δ13CH4) are also reported for a subset of the sites. Measurements were reported following the WMO X2004A scale for CH4 and the WMO X2019 scale for CO2. CRDS instruments were calibrated for CH4 and CO2 in the laboratory prior to deployment. For H2S, data were offset-corrected using the minimum 40 min running mean value of the day, and for δ13CH4, calibrations were based on laboratory data. We describe the characteristics of the dataset with a set of illustrative analyses. Methane and carbon dioxide showed strong seasonality, with a well-defined diurnal cycle during the summer, which was opposed to the winter, when a diurnal cycle was absent. CH4 enhancements to the background, during the winter, are up to twice the summer values, which is attributed to the changes in boundary layer depth and wind speed. The largest CH4 enhancements occurred when winds blow from the center of the Delaware sub-basin, where most of the methane emissions come from. The magnitude of enhancements of CO2 did not present seasonality. H2S enhancements indicated a potential source northeast of the tower (Hobbs, New Mexico) where the inlet is installed. Isotopic ratios of methane indicated that oil and natural gas extraction is the source of local methane in the region. The hourly-averaged data, starting on 1 March 2020 and described in this paper, are archived at The Pennsylvania State University Data Commons at https://doi.org/10.26208/98y5-t941 (Monteiro et al., 2021).

The impact of the COVID-19 lockdown on greenhouse gases: a multi-city analysis of in situ atmospheric observations

We tested the capabilities of urban greenhouse gas (GHG) measurement networks to detect abrupt changes in emissions, such as those caused by the roughly 6-week COVID-19 lockdown in March 2020 using hourly in situ GHG mole fraction measurements from six North American cities. We compared observed changes in CO2, CO, and CH4 for different mole fraction metrics (diurnal amplitude, vertical gradients, enhancements, within-hour variances, and multi-gas enhancement ratios) during 2020 relative to previous years for three periods: pre-lockdown, lockdown, and ongoing recovery. The networks showed decreases in CO2 and CO metrics during the lockdown period in all cities for all metrics, while changes in the CH4 metrics were variable across cities and not statistically significant. Traffic decreases in 2020 were correlated with the changes in GHG metrics, whereas changes in meteorology and biology were not, implying that decreases in the CO2 and CO metrics were related to reduced emissions from traffic and demonstrating the sensitivity of these tower networks to rapid changes in urban emissions. The enhancements showed signatures of the lockdowns more consistently than the three micrometeorological methods, possibly because the urban measurements are collected at relatively high altitudes to be sensitive to whole-city emissions. This suggests that urban observatories might benefit from a mixture of measurement altitudes to improve observational network sensitivity to both city-scale and more local fluxes.

Continuous CH<sub>4</sub> and <i>δ</i><sup>13</sup>CH<sub>4</sub> measurements in London demonstrate under-reported natural gas leakage

Abstract. Top-down greenhouse gas measurements can be used to independently assess the accuracy of bottom-up emission estimates. We report atmospheric methane (CH4) mole fractions and δ13CH4 measurements from Imperial College London from early 2018 onwards using a Picarro G2201-i analyser. Measurements from March 2018 to October 2020 were compared to simulations of CH4 mole fractions and δ13CH4 produced using the NAME (Numerical Atmospheric-dispersion Modelling Environment) dispersion model coupled with the UK National Atmospheric Emissions Inventory, UK NAEI, and a global inventory, the Emissions Database for Global Atmospheric Research (EDGAR), with model spatial resolutions of ∼ 2, ∼ 10, and ∼ 25 km. Simulation–measurement comparisons are used to evaluate London emissions and the source apportionment in the global (EDGAR) and UK national (NAEI) emission inventories. Observed mole fractions were underestimated by 30 %–35 % in the NAEI simulations. In contrast, a good correspondence between observations and EDGAR simulations was seen. There was no correlation between the measured and simulated δ13CH4 values for either NAEI or EDGAR, however, suggesting the inventories' sectoral attributions are incorrect. On average, natural gas sources accounted for 20 %–28 % of the above background CH4 in the NAEI simulations and only 6 %–9 % in the EDGAR simulations. In contrast, nearly 84 % of isotopic source values calculated by Keeling plot analysis (using measurement data from the afternoon) of individual pollution events were higher than −45 ‰, suggesting the primary CH4 sources in London are actually natural gas leaks. The simulation–observation comparison of CH4 mole fractions suggests that total emissions in London are much higher than the NAEI estimate (0.04 Tg CH4 yr−1) but close to, or slightly lower than, the EDGAR estimate (0.10 Tg CH4 yr−1). However, the simulation–observation comparison of δ13CH4 and the Keeling plot results indicate that emissions due to natural gas leaks in London are being underestimated in both the UK NAEI and EDGAR.

Ferric-carbon micro-electrolysis and zeolite reduce CH4 and N2O emissions from the aerated constructed wetland

Aeration has been widely used in constructed wetland (CWs). However, research on greenhouse gas (GHG) emissions and measures to control GHG emissions in aerated CWs is still limited. Therefore, lab-scale aerated CWs were established in this study to explore effects of Fe–C and zeolite on GHG emissions from aerated CWs. Four groups of CWs were filled with gravel (CW-A), zeolite (CW–B), ferric-carbon micro-electrolytic filler (Fe–C) and gravel (CW–C) and Fe–C and zeolite (CW-D). The results showed that compared with CW-A, the other CWs reduced CH4 emissions by 24.39%–51.22%. N2O emissions from CW-C and CW-D were on average 48.53% and 58.20% lower than those from CW-A, respectively, because Fe–C significantly changed abundance of functional genes. Overall, combined use of Fe–C and zeolite as substrate is recommended to optimize aerated CWs, which simultaneously achieved the best treatment performance and the lowest GHG emissions.

New York City greenhouse gas emissions estimated with inverse modeling of aircraft measurements

Cities are greenhouse gas emission hot spots, making them targets for emission reduction policies. Effective emission reduction policies must be supported by accurate and transparent emissions accounting. Top-down approaches to emissions estimation, based on atmospheric greenhouse gas measurements, are an important and complementary tool to assess, improve, and update the emission inventories on which policy decisions are based and assessed. In this study, we present results from 9 research flights measuring CO2 and CH4 around New York City during the nongrowing seasons of 2018–2020. We used an ensemble of dispersion model runs in a Bayesian inverse modeling framework to derive campaign-average posterior emission estimates for the New York–Newark, NJ, urban area of (125 ± 39) kmol CO2 s–1 and (0.62 ± 0.19) kmol CH4 s–1 (reported as mean ± 1σ variability across the nine flights). We also derived emission estimates of (45 ± 18) kmol CO2 s–1 and (0.20 ± 0.07) kmol CH4 s–1 for the 5 boroughs of New York City. These emission rates, among the first top-down estimates for New York City, are consistent with inventory estimates for CO2 but are 2.4 times larger than the gridded EPA CH4 inventory, consistent with previous work suggesting CH4 emissions from cities throughout the northeast United States are currently underestimated.

Differential Absorption Lidar (DIAL) Measurements of Pollutants and Greenhouse Gases from Industrial Emissions

Differential Absorption Lidar (DIAL) Measurements of Pollutants and Greenhouse Gases from Industrial Emissions

Sensors and Methods for Measuring Greenhouse Gas Emissions from Different Components of Livestock Production Facilities

Greenhouse gas monitoring on a broader scale is necessary to ensure that a cap-and-trade system is effective, reduces measurement uncertainty, and detects fraudulent or illegal activities. The recent strict air quality regulation in livestock production facilities has accelerated the need for accurate on-farm determination of greenhouse gas (GHG) emission rates (ERs) from livestock operations in the United States under a wide range of production, management, and climate conditions. The estimation of GHG emissions from different ground-level sources or at a property line is a very complicated process, and such measurements require multidirectional expertise including engineering, micrometeorology, agronomy, applied physics, and chemistry. Accurate measurement of gaseous concentration from an emitting source is a prerequisite and of paramount importance for estimating emissions rates (ERs) using any micro-meteorological and sampling device-based method. This paper provides an overview of the state-of-the-art sensors and analyzers used to measure GHG concentrations. Sensor and analyzer selection and their performance in the laboratory and field were discussed. In addition, protocols for data quality control (QC) and quality assurance (QA) when deploying sensors in the area for long-term use were also discussed. In addition, the preparation of measurement systems, coupling of air samplers with sensing systems for measuring gaseous concentrations, and uncertainties inherent to such measurement methods as a whole to estimate ERs were discussed in this paper.

Measurement report: Regional characteristics of seasonal and long-term variations in greenhouse gases at Nainital, India, and Comilla, Bangladesh

Abstract. Emissions of greenhouse gases (GHGs) from the Indian subcontinent have increased during the last 20 years along with rapid economic growth; however, there remains a paucity of GHG measurements for policy-relevant research. In northern India and Bangladesh, agricultural activities are considered to play an important role in GHG concentrations in the atmosphere. We performed weekly air sampling at Nainital (NTL) in northern India and Comilla (CLA) in Bangladesh from 2006 and 2012, respectively. Air samples were analyzed for dry-air gas mole fractions of CO2, CH4, CO, H2, N2O, and SF6 and carbon and oxygen isotopic ratios of CO2 (δ13C-CO2 and δ18O-CO2). Regional characteristics of these components over the Indo-Gangetic Plain are discussed compared to data from other Indian sites and Mauna Loa, Hawaii (MLO), which is representative of marine background air. We found that the CO2 mole fraction at CLA had two seasonal minima in February–March and September, corresponding to crop cultivation activities that depend on regional climatic conditions. Although NTL had only one clear minimum in September, the carbon isotopic signature suggested that photosynthetic CO2 absorption by crops cultivated in each season contributes differently to lower CO2 mole fractions at both sites. The CH4 mole fraction of NTL and CLA in August–October showed high values (i.e., sometimes over 4000 ppb at CLA), mainly due to the influence of CH4 emissions from the paddy fields. High CH4 mole fractions sustained over months at CLA were a characteristic feature on the Indo-Gangetic Plain, which were affected by both the local emission and air mass transport. The CO mole fractions at NTL were also high and showed peaks in May and October, while CLA had much higher peaks in October–March due to the influence of human activities such as emissions from biomass burning and brick production. The N2O mole fractions at NTL and CLA increased in June–August and November–February, which coincided with the application of nitrogen fertilizer and the burning of biomass such as the harvest residues and dung for domestic cooking. Based on H2 seasonal variation at both sites, it appeared that the emissions in this region were related to biomass burning in addition to production from the reaction of OH and CH4. The SF6 mole fraction was similar to that at MLO, suggesting that there were few anthropogenic SF6 emission sources in the district. The variability of the CO2 growth rate at NTL was different from the variability in the CO2 growth rate at MLO, which is more closely linked to the El Niño–Southern Oscillation (ENSO). In addition, the growth rates of the CH4 and SF6 mole fractions at NTL showed an anticorrelation with those at MLO, indicating that the frequency of southerly air masses strongly influenced these mole fractions. These findings showed that rather large regional climatic conditions considerably controlled interannual variations in GHGs, δ13C-CO2, and δ18O-CO2 through changes in precipitation and air mass.

How digital technologies can reduce greenhouse gas emissions in the energy sector's legacy assets

The global community is increasingly committed to transitioning to green energy technologies. However, while the percentage of the worldʼs energy coming from renewables is growing, the absolute amount of energy delivered to the global marketplace in the form of fossil fuels is also getting bigger, causing the International Energy Agency to recently declare that “it is too soon to see a rapid decline of oil.” This realization carries with it some sobering perspective about what needs to be done by the energy industry to mitigate climate change. Based on a keynote address delivered at the United Nations’ “Resource Management Week 2021” conference, this viewpoint argues that, in tandem to sowing the seeds of tomorrow's renewable energy systems, we also need to reduce the emissions from the systems that we have right now because the evidence in front of us strongly suggests that these legacy energy sources will continue to be around for the short- to medium-term future. To this end, this paper highlights four digital technological developments that have the potential to significantly help the oil & gas industry to make progress on this front: (1) continuing the industry's journey to “smartness,” (2) edge computing, (3) the emergence of global data standards for measuring greenhouse gas emissions, and (4) improving the efficiency of digital infrastructure.

Checking the progress of using the static chamber method for the measurement of greenhouse gases in Latin America

Manual static chamber is one of the most widespread methods for the quantification of greenhouse gases (GHGs) emissions from agricultural systems. But there are concerns about the reliability of measurements and a necessity to assess the static chambers used in the studies performed in the countries of Latin America. Thus, this study aims to investigate the quality of the characteristics from the static chamber methodology, the confidence level of the GHG measurements, and recommend what should be improved. We conducted a systematic review of databases to identify peer-reviewed articles that used the static chamber method in Latin America. A total of 90 articles were analyzed and separated according to the publication year (2000-2008, 2009-2015, 2016-2020). We evaluated eight design and deployment chamber characteristics. The depth of base insertion and type of storage vial received the lowest scores, and the number of samples received the highest score. The description and reporting of the methodological procedures in the studies should be improved. The percentage of articles with high and medium confidence levels increased within the time, and the number of articles with low and very low confidence levels reduced. Scientists/Researchers should continue to follow the protocols, especially the most updated ones.

Comparing Soil Nitrous Oxide and Methane Fluxes From Oil Palm Plantations and Adjacent Riparian Forests in Malaysian Borneo

Riparian forests are often kept as buffers between rivers and oil palm plantations. Many benefits of riparian forests, such as increasing biodiversity and providing a travel corridor for wildlife have been documented. Conversely, data on fluxes of the greenhouse gases nitrous oxide (N2O) and methane (CH4) from riparian forests are sparse. Nitrogen (N) from fertilizer applied in the oil palm plantations leached to the adjacent riparian forests, may increase emissions of N2O. Methane (CH4) fluxes might also differ between oil palm plantations and riparian forests due to carbon (C) availability. In this scoping study, we installed transects from three mature oil palm plantations to adjacent riparian forests within the SAFE project landscape in Sabah, Malaysia (https://www.safeproject.net) for measurements of greenhouse gases and associated parameters every 2 months for 13 months. Emissions of N2O were higher from riparian forests with 40.4 [95% confidence intervals (CI): 35.7–44.6] μg N2O-N m–2 h–1 than from an equivalent area of oil palm plantation 27.6 (CI: 23.1–32.3) μg N2O-N m–2 h–1. Methane uptake was significantly higher from the riparian forest with −14.7 (CI: −21.1 to −8.3) μg CH4-C m–2 h–1 compared to slight positive emission in the oil palm plantations of 6.3 (CI: 1.1–11.4) μg CH4-C m–2 h–1. We are contributing urgently needed flux data for less well studied riparian forests in the Tropics, however, additional long-term studies are needed to be able to draw wider conclusions than possible from this scoping study alone.

A purposeful approach for measuring greenhouse gas emissions of material flow accounts for the accomplishment of territorial sustainable development and cultural economy goals on climate. The case of the Basque Country

This study aims at developing a purposeful approach for estimating greenhouse gas (GHG) emissions and its possible use to recreate alternative scenarios that might potentially facilitate the attainment of the material productivity (MP) ratio needed for achieving territorial sustainable development (SDGs) and circular economy goals on climate. The propounded method associates these two key concepts (GHG-MP) with the domestic material consumption (DMC) and international trade of materials, including product life cycle emissions in the overarching GHG total estimation. Developed utilizing the United Nations Framework Convention on Climate Change (UNFCCC) and diverse data, linked to the suggested scheme, from the Basque Country (Spain), this work also relies its scientific foundation upon leading literature in this field to align territorial models of production and consumption with a more localized measurement of GHG emissions. According to its results, the emissions estimated allow advising more contextualized scenarios for the potential achievement of local MP target indicator, when expressed as the amount of economic output―based on gross domestic product (GDP)—generated per unit of materials consumed and traded―in terms of DMC. From a theoretical perspective, this work contributes to the local strategic management of circular economy research and 2030 Agenda, particularly on the subject of measuring progress in the achievement of territorial climate and circular economy goals. From a utilitarian perspective, the findings comprise promising implications for both multilevel policy makers and public/private organizations that further sustainable development and actions against climate change.

The role of energy policy on the decoupling processes in the European Union countries

The study offers thorough analysis of the impact of the European Union (EU) energy policy on decoupling greenhouse gas (GHG) emissions from economic growth between 1996 and 2017. Two types of GHG measurements, production-based accounting (PBA) and consumption-based accounting (CBA), are used to account for the possible outsourcing with the Tapio framework. Five factors taken from the Log-Mean Divisia Index are considered in order to determine the main contributors of emission mitigation.The results demonstrate decoupling GHG emissions from economic growth in almost all countries, regardless of the type of GHG measurements. However, in the case of production-based emissions, the decoupling occurs faster. After 2005, when the EU launches its energy policy, the decoupling speeds up. LMDI results indicate that the improvements in energy intensity and the energy structure are the most significant drivers of GHG emissions reduction. There are differences between the reduction of the two types of GHG emissions and its determinants in old and new EU countries.In almost all EU countries the decoupling is linked to the EU energy policy but the reduction of GHG emissions partly comes at the expense of outsourcing, i.e. the relocation of emission-intensive industries to countries outside the EU.

Greenhouse gas emissions from Mediterranean agriculture: Evidence of unbalanced research efforts and knowledge gaps

Designing effective mitigation policies for greenhouse gas (GHG) emissions from agriculture requires understanding the mechanisms by which management practices affect emissions in different agroclimatic conditions. Agricultural GHG emissions and carbon sequestration potentials have been extensively studied in the Mediterranean biome, which is a biodiversity hot spot that is highly vulnerable to environmental changes. However, the absolute magnitude of GHG emissions and the extent to which research efforts match these emissions in each production system, are unknown. Here, we estimated GHG emissions and potential carbon sinks associated with crop and livestock production systems in the Mediterranean biome, covering 31 countries and assessing approximately 10,000 emission items. The results were then combined with a bibliometric assessment of 797 research publications to compare emissions estimates obtained with research efforts for each of the studied items. Although the magnitude of GHG emissions from crop production and the associated carbon sequestration potential (261 Tg CO2eq yr−1) were nearly half of those from livestock production (367 Tg CO2eq yr−1), mitigation research efforts were largely focused on the former. As a result, the relative research intensity, which relates the number of publications to the magnitude of emissions, is nearly one order of magnitude higher for crop production than for livestock production (2.6 and 0.4 papers Tg CO2eq−1, respectively). Moreover, this mismatch is even higher when crop and livestock types are studied separately, which indicates major research gaps associated with grassland and many strategic crop types, such as fruit tree orchards, fiber crops, roots and tubers. Most life cycle assessment studies do not consider carbon sequestration, although this single process has the highest magnitude in terms of annual CO2eq. In addition, these studies employ Tier 1 IPCC factors, which are not suited for use in Mediterranean environments. Our analytical results show that a strategic plan is required to extend on-site field GHG measurements to the Mediterranean biome. Such a plan needs to be cocreated among stakeholders and should be based on refocusing research efforts to GHG balance components that have been afforded less attention. In addition, the outcomes of Mediterranean field studies should be integrated into life cycle assessment-based carbon footprint analyses in order to avoid misleading conclusions.

Analysis of the Relationship of the Degree of Aviation Sector Development with Greenhouse Gas Emissions and Measures of Economic Development in the European Union Countries

The rapid growth of aviation over the past fifty years has resulted in numerous negative environmental impacts due to the combustion of fossil fuels in aircraft engines. This paper presents the relationship between air transport and GHG emissions. Based on data on the development of aviation, the level of GHG emissions from transport, environmental tax revenues and the amount of GDP per capita in the countries of the European Union, an attempt was made to create a typification that would illustrate the interaction of GHG emissions with air transport, environmental taxes and GDP in the years 2009–2018. The next step to confirm the obtained results was the application of statistical methods: the TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) method of linear ordering and the Perkal index. Based on the study findings, the analyzed countries were divided into three groups: the group of innovators, the stable group and the group of students. The analysis revealed the relationship of all three analyzed variables with air transport. The development of the aviation sector leads to a significant increase in GHG emissions from transport, increased revenues from environmental taxes and acceleration of the rate of economic growth of a country.

CO2 and N2 O emissions and microbial community structure from fields that include salt-affected soils.

Although salinity and sodicity are worldwide problems, information on greenhouse gas (GHG) emissions from agricultural salt-affected soils is scarce. The CO2 -C and N2 O-N emissions were quantified from three zones intertwined within a single U.S. northern Great Plains field: a highly productive zone (electrical conductivity with 1:1 soil/water mass ratio [EC1:1 ]=0.4 dS m-1 ; sodium adsorption ratio [SAR]=1.8), a transition zone (moderately salt-affected; EC1:1 =1.6 dS m-1 ; SAR=4.99), and a saline/sodic zone (EC1:1 =3.9 dS m-1 ; SAR=22). In each zone, emissions were measured every 4h for 7 d in four randomly placed chambers that were treated with two N rates (0 and 224kg N ha-1 ). The experiment was conducted in 2018 and 2019 during similar seasonal periods. Soil samples taken from treatments after GHG measurement were analyzed for soil inorganic N, and microbial biomass from different communities was quantified using phospholipid fatty acid analysis. Real-time polymerase chain reaction was used to quantify the number of copies of some specific denitrification functional genes. The productive zone had the highest CO2 -C, the lowest N2 O-N emissions, and the greatest microbial biomass, whereas the saline/sodic zone had the lowest CO2 -C, the highest N2 O-N emissions, and the lowest microbial biomass. Within a zone, urea application did not influence CO2 -C emissions; however, N2 O-N emissions from the urea-treated saline/sodic zone were 84 and 57% higher than from the urea-treated productive zone in 2018 and 2019, respectively. The copy number of the nitrite reductase gene, nirS, was 42-fold higher in the saline/sodic zone than in the productive soil, suggesting that the saline/sodic soil had a high potential for denitrification. These findings suggest N2 O-N emissions could be reduced by not applying N to saline/sodic zones.

Local emission and long-range transport impacts on the CO, CO2, and CH4 concentrations at a tropical rural site

Local emission and long-range transport impacts on the observed concentrations (dry air mole fractions) of CO, CO2, and CH4 have been investigated using three years (April 2016 to April 2019) of surface measurements at a tropical rural site, Gadanki (13.5° N, 79.2° E) in Southern peninsular India. Gadanki represents the poor coverage area of Greenhouse Gas (GHG) measurements in India and has both local emission and long-range transport influences on its air masses. All the three gases have shown strong seasonality and diurnal variations. Trend analysis showed a significant decreasing trend in CO (14.3 ± 0.2 ppbv/year) and increasing trends in CO2 (2.5 ± 1.2 ppmv/year) and CH4 (11.1 ± 0.03 ppbv/year). CO2 and CH4 trends are marginally higher than the global trends (2.2 ± 0.004 ppmv/year and 7.0 ± 0.001 ppbv/year, respectively) for the same period highlighting the sustained local emission impact on the observed concentrations. Among the three species, CO has been the most local emission impacted species with local emission contribution (to the total observed concentration) varying between 4 and 25% during different seasons with a median value always lying above 10% irrespective of the season. In the case of CO2 and CH4, the local emission contribution found to vary in the range of 0.8–7% and 0.15–3%, respectively. Long-range transport impact dominance over the local emission is observed in CO2 and CH4 during all the seasons. Analysis using MODIS fire count data, Concentration Weighted Trajectory (CWT) and FLEXPART have reconfirmed the combined effect of local and long-range transport impacts on the observed concentrations. Comparison of the IASI MetOp and AIRS satellite data products with surface measurements showed the significant bias and poor representation of the seasonality demonstrating the limitations on the sensitivity of satellite trace gas measurements within the boundary layer.

Simultaneous tree stem and soil greenhouse gas (CO2 , CH4 , N2 O) flux measurements: a novel design for continuous monitoring towards improving flux estimates and temporal resolution.

Tree stems and soils can act as sources and sinks for the greenhouse gases (GHG) carbon dioxide (CO2 ), methane (CH4 ), and nitrous oxide (N2 O). Since both uptake and emission capacities can be large, especially in tropical rainforests, accurate assessments of the magnitudes and temporal variations of stem and soil GHG fluxes are required. We designed a new flexible stem chamber system for continuously measuring GHG fluxes in a French Guianese rainforest. Here, we describe this new system, which is connected to an automated soil GHG flux system, and discuss measurement uncertainty and potential error sources. In line with findings for soil GHG flux estimates, we demonstrated that lengthening the stem chamber closure time was required for accurate estimates of tree stem CH4 and N2 O flux but not tree stem CO2 flux. The instrumented stem was a net source of CO2 and CH4 and a weak sink of N2 O. Our experimental setup operated successfully in situ and provided continuous tree and soil GHG measurements at a high temporal resolution over an 11-month period. This automated system is a major step forward in the measurement of GHG fluxes in stems and the atmosphere concurrently with soil GHG fluxes in tropical forest ecosystems.